This invention relates in general to fuel injection systems in internal combustion piston engines and more particularly it relates to a stratified charge hybrid type engine having dual injectors, one in the prechamber and the other one in the main chamber, and a single engine driven and timed injection pump providing for both injectors in sequential order and a trigger for timed spark ignition. The engine is hybrid in the sense of having transitional combustion modes from spark-ignited stratified charge mode at lower power, to a spark-assisted compression ignition at higher power loads and a compression ignition mode at maximum power loads. The engine is a low compression engine which burns turbine fuels and has no specific octane or cetane requirements. The engine is described in further detail in U.S. Pat. No. 4,594,976 and in U.S. Pat. No. 4,765,293.
Stratified charge engines which include pilot chambers and main chambers have been in existence for over 50 years as exemplified by the Ricardo U.S. Pat. No. 2,191,042. These type of engines, in isolated cases, have successfully operated with turbine fuels, however, they have been in ground transportation applications of low specific power output types.
A number of prior art patents utilize dual injectors which are ignited by an electrical spark as typified by Hoffman, U.S. Pat. No. 2,902,011 and Loyd U.S. Pat. No. 4,141,940. Both of the latter mentioned engines are low specific power output engines that require relatively wide injection timing spreads between pilot and main chambers of approximately 40.degree. which limits the power and speed capabilities of the engine.
The patent to Nallinger (U.S. Pat. No. 2,914,043) also teaches a stratified charge dual injector system which are supplied by a single pump. This engine is strictly a gasoline engine with the fuel injection system operating at low pressures and is not configured to operate on a diesel or hybrid mode. The Nallinger engine is of an early injection timing type and requires fuels that provide a measure of detonation or autoignition control on combustion, and therefore require octane rated fuels. The Nallinger engine is clearly not configured to operate in a diesel or hybrid mode. The injection system of the present invention is considered a late injection system (main injection starts at approximately 10.degree. BTDC, while pilot injection starts begins at approximately 30.degree. BTDC). Later injection, of course, requires higher injection pressures as in conventional diesel engines.
U.S. Pat. No. 4,239,023 to Simko describes a dual injection system utilized in a pilot or prechamber and main chamber. However, this early injection timing engine is a strictly spark-ignition low output engine based on turbulent flow conditions in both the prechamber and main chamber cavities, while the late-timed engine of the present invention depends upon well organized swirl conditions in both chambers. Both the present invention and Simko are similar in that they both utilize a shuttle valve between the injectors in the prechamber and main chamber, however, the response time with applicant's shuttle valve is shorter and more precise than Simko which includes a variety of slow moving check valves which affect the overall reaction time and timing precision of the system.
A similar stratified charge low-compression turbine fueled experimental engine is being developed by White Engines, Inc. and Texaco, Inc. referred to as the L-163-ST engine (Road and Track, November 1979, pages 39 and 40). The White engine above-mentioned does not include a separate prechamber but rather locates the spark plug in the main chamber and achieves stratification by closely locating the injector to the spark plug.
In SAE Technical Paper No. 830666 titled "The Pencil Nozzle--Past, Present and Future" dated Feb. 28-Mar. 4 1983, illustrates the concept of an ignition-triggering nozzle on page 24, wherein the opening of the nozzle due to pressure rises within the nozzle electrically fires the ignition system in place of a separate ignition distribution system.
The injection system of the present invention includes a novel ignition triggering means in the shuttle valve which fires the spark plug in the prechamber which is not taught by any of the above-mentioned prior art.